In situ combustion of carbonaceous deposits



March 29, 1960 H. W. PARKER IN SITU COMBUSTION OF CARBONACEOUS DEPOSITS Filed Aug. 26, 1957 AIR OR COMBUSTIBLE BEARING STRATUM MIXTURE INVENTOR.

A TTORNEYS 1N SITU COMBUTION (IARBQNACEOUS DEPOSITS Barry W. Parker, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware.

Application August 26, 1957, Serial No. 680,297

8 Claims. (Cl. 262-3) This invention relates to a process for initiating in situ combustion in a stratum containing hydrocarbon material and for recovering hydrocarbon material therefrom.

in situ combustion in the recovery of oil from underground strata containing the same is becoming increasingly important in the production of petroleum hydrocarbons. Several problems have been encountered in practicing in situ combustion in hydrocarbon production. in hydrocarbon-bearing shale deposits, the permeability of the formation is usually so low that gases cannot be made to pass thru the formation even at relatively high pressures thereby rendering in situ combustion extremely difficult. In permeable strata the movement of the combustion front away from the borehole around which combustion is initiated by direct injection of combustion-supporting gas into the borehole builds up a wall or bank of heavy hydrocarbon liquid ahead of the advancing combustion-front so that the fire dies out from lack of oxygen. One method of overcoming this difiiculty of plugging the stratum around the initial fire hole is disclosed in the copending application of John W. Marx, owned by the assignee of the present invention, Serial No. 526,388,filed August 4, 1955, now abandoned. The problem of plugging and building up a liquid bank in the area in front of the combustion zone is recognized in US. Patent 2,793,696 and the process disclosed and claimed therein is necessarily limited toformations which contain no oil displaceable by gas fiow so that initiation of the combustion zone and expansion thereof to permit establishment of inverse air injection does not build up a bank of liquid oil which shuts off How thru the stratum.

The present invention is concerned principally with a process which avoids the problems of in situ combustion outlined above.

Accordingly, it is an object of the invention to provide an improved in situ combustion process for recovering hydrocarbons from a stratum containing the same. Anothn' object is to provide an improved in situ combustion process for recovering hydrocarbons from shale. A further object is to provide an improved method of initiating combustion in a stratum containing hydrocarbon material It is, also,-an object of the invention to provide a process for initiating combustion in an oil bearing stratum which avoids formation of a bank of heavy liquid around the combustion zone and which keeps the stratum open to gas flow. Other objects will become apparent from a consideration of the accompanying disclosure.

in its broadest aspect, the invention comprises burning a combustible gaseous mixture in a borehole in a hydrocarbon-containing stratum so as to heat up the stratum to combustion supporting temperature and while the formation is at this temperature increasing the proportion of free oxygen in the combustible mixture so as to initiate in situ combustion and withdrawing the combustion products and produced hydrocarbon from the borehole thru which the combustion is initiated. In order to facilitate the combustion process, the borehole around the injection tubing within the oil-bearing stratum is packed with particulate refractory material such as sand, gravel, chat, vermiculite, refractory ceramic, broken fire brick, pumice, pebbles,"consolidated particles of clay, or any other highly refractory particulate material. An oxidation catalyst may be incoporated in the granular material as an aid in starting combustion of hydrocarbon in the stratum. The packing material in the form of an annulus around the injection tubing provides a pressure gradient thruthe producing zone which materially reduces bypassing the'oxygen (air) up the borehole without con-' tacting the hydrocarbon material in the formation.

After a substantial area of the stratum has been heated by combustion of hydrocarbon in place, the combustion front may be readily advanced thru the stratum substantially horizontally therein to surrounding spaced boreholes by gas drive with a free-oxygen containing gas. This gas drive is preferably elfected by inverse air injection thru one or more surrounding boreholes extending into the stratum. In most formations, movement of the combustion front by direct gas drive from the borehole around which combustion was initiated is impossible because of the buildup of a liquid bank in the formation ahead of the front which shuts off the flow of gas and therefore the supply of oxygen. Strata in which there is no substantial buildup of liquid hydrocarbons ahead of the combustion front with concomitant plugging of the formation are the exception and, hence, in most cases it is essential to utilize inverse air injection to propagate the combustion front.

My method of initiating a combustion process and establishing a substantial combustion zone around a borehole wherein the combustion products and produced hydrocarbons are withdrawn from the borehole around which the combustion is initiated substantially avoids plugging of the formation outside of the combustion zone because of the fact that gases are not being forcedinto the stratum by high gas pressures and, therefore, liquid hydrocarbons produced by the combustion flow into the borehole and can be produced or removed therefrom by conventional methods. has been established around the borehole, it is relatively simple to pass a combustion supporting gas, such as air, from surrounding boreholes in the oil bearing stratum to the combustion zone so as to effect the advancement of the combustion front toward the injection wells or, if the formation is susceptible to direct drive of the combustion front by direct air injection from the borehole aroundwhich combustion has been established, this procedure may be followed.

In order to provide a more complete understanding of the invention, reference is made to the accompanying schematic drawing which shows an elevation of one arrangement of apparatus or equipment in relation to boreholes in an oil-bearing stratum for operation in accordance with the invention. A pair of boreholes or wells Ill and 12 extend thru an oil-bearing stratum 14. Each well is provided with a casing 116. Well or borehole 12 is provided withjtubing 18 for the injection of air and/or a Patented Mar. 29, 1950 After a substantial heat reservoir combustible mixture of'fuel' and air. (lt is to be understood that any free-oxygen-containing gas of high enough 0 concentration to support combustion may be used in lieu of air.) A takeoff line 29 for exit gases connects with the well casing. Tubing 18 is provided with a screen 22 near the lower end thereof which passes combustible gas but prevents burn-back into the tubing and explosion therein. It is also feasible to utilize an additional conduit either concentric with conduit 13 or outside thereof to inject either air or fuel gas so that the mixing takes place at the level of the oil bearing stratum. Suitable means for igniting the combustible mixture in the form of a squib or electrical starting device (not shown) may beprovided at the lower end of the tubing.

The borehole, coextensive with the-oil-bearing stratum 14 ispacked with particulate refractory material 24.. This packing material assists in forcing oxygen containing gas in contact with the hydrocarbon in place in the stratum and cuts down on bypassing of the oxygen thru the borehole. Numeral 26 represents the 'spent zone in the stratum surrounding borehole 12 after combustion of the in-place hydrocarbon to at least partially deplete the sand, limestone, or shale formation, leaving the stratum substantially more porous than before the combustion was effected.

air all along the face of: the borehole within the stratum.

in operation inimpervious oil-bearing shale; a combustile mixture of fuel gas and air (or other free oxygencontaining gas) is injected and burnedwithin the borehole adjacent the shale until the temperature (ascertained by. suitable location of thermostats not shown) of the shale, reaches a combustion supporting temperature such as 400 to 700 F. at whichtime the injection of fuel is gradually cut off or completely reduced immediately so that free oxygen is available for burning hydrocarbon in place in the shale. Continued injection of free oxygen expands the combustion zone and drives volatilized hydrocarbon material from the shale. It is also feasible to inject a small amount of Water with the airsupply so as to. control the temperature of the injection tubing and reduce the amount of air by-passing the combustion zone. The injection of cold air as the combustion supporting gas creates a zone of a lower temperature adjacent the injection tubing so that the gas in the wellbore around the tubing is of higher density than the gas farther out in the formation. This helps to cause a greater proportion of air to flow upwardly thru thev hot edge of the combustion front in preference to the shorter vertical path thru the borehole.

If the formation is substantially impervious to gas fiow', such as is the case in a shale'formation; the formationmay be fractured between spaced apart wells prior to the initiation of combustion so that after theestablishment of the expanded combustion zone the combustion zone may be driven thru the formation along the fractures to the surrounding boreholes by either direct or inverse air injection. The flow of gas and drive of the combustion front thru the fractures may beprevented by maintaining the valves in conduits 20 and 28 of borehole it) closed until such time as it is desired to move the combustion area toward'this borehole thru the fractures. With direct injection of airQproduction is recovered thru efiluent line 20 of borehole 1t and it is feasible to utilize an imperforate conduit 28 for recovery of liquid products by conventional methods. Where inverse injection of air thru conduit 28 is utilized, combustion products and hydrocarbon are taken off thru lines 18 and/or 20 of borehole 12.

In relatively permeable formations, fracturing is not essential to movement of the combustion front from the vicinity of borehole 12 to the surrounding wells 10, it being feasible to merely inject air thru conduit 28 into borehole 10 from which the air passes thru the stratum the following test was made. a deep was drilled into thetop of a lump of medium grade to the combustion front established around borehole 12 oil shale 5".by 9" and 6 /2" thick. Provision was made to admit air to the bottom of'the hole through a A5" f O.D. tube in the borehole and to conduct the gases coming up the annulus to a condenser. The lower inch of the tube had anelectric heater wound around it. The well bore annulus was filled with -100 mesh sand. The outside of the block was plastered with Portland cement and then wrapped with electric heating tapes and insulation.

To compensate for the high heat losses found in this small system the lump of shale was preheated by means of the heating tapes to 260, F. Air was supplied to the center jtube'at4-5 s.c.f.h. Powerwas applied'in increasing amounts to the heater in the well. until ignition occurred at which time the power input remained constant. The sudden rise in temperature of a thermocouple just above the heater showed when ignition occurred. This temperature was held below 1000 F. by decreasing the air rate to about 0.5 s.c.f.h. Combustion was maintained in this manner for about three hours. Examination of the resulting block of shale showed a zone 1%" maximum diameter and 2%" long had been affected by the heat. The central portion of this zone had the carbon burned from it showing combustion had occurred in the shale. T he fact that increased air rates increased the well bore temperature also showed that combustion was occurring. Little product was collected since cracks developed in the plaster around the shale letting the exit gases escape instead of going to the condenser. V

This work was of a qualitative nature but shows that combustion can be caused to occur in impermeable oil shale by the process of the invention.

Certain modifications'of the invention willbecome ap parent to those skilled. in the art and the illustrative details disclosed are not to be construed as imposing unneccessary limitations on the invention.

I claim: I

l. A process for initiating in situ combustion in an underground stratum containing hydrocarbon material comprising providing a borehole extending to a lower level of said stratum and a tubing string therein extending to adjacent said level; packing the annulus around the lower end of said tithing with particulate refractory material to an upper level of said stratum; passing a com-' tory material minimizing lay-passing of oxygen thru said annulus and forcing same to pass thru the combustion zone withinsaid stratum after combustion has been initiated; and recovering produced hydrocarbons from said borehole.

'2. The process of claim 1 wherein said stratum is a relatively impervious shale.

' 3. The process of claim 1 wherein a small but effective amountof water is introduced thru said conduit to cool same and to reduce the amount of combustion zone.

4. The process of claim 1 wherein the oxygen is supplied in the form of cold air.

5. The process of claim 1 wherein the burning of hydrocarbon material is continued until a substantial area surrounding said borehole has been burned and raised to a temperature substantially above a minimum combustion-supporting temperature; thereafter driving the resulting combustion front thru said stratum to at least one other borehole therein by gas drive with a free oxygencontaining gas.

6. The process of claim 5 wherein the combustion front is driven thru said stratum by injection of air thru said at least one other borehole.

7. The process of claim 6 wherein the combustion front is driven thru said stratum by injection of air thru said first borehole.

8. The process of claim 5 wherein said stratum is a air lay-passing the 6 relatively impervious shale and including the steps of fracturing and propping of same prior to initiation of combustion in the stratum.

References Cited in the file of this patent UNITED STATES PATENTS 2,596,845 Clark May 15, 1952 2,630,307 Martin Mar. 3, 1953 2,688,464 Payne Sept. 7, 1954 2,780,449 Fisher et al Feb. 5, 1957 2,786,660 Alleman Mar. 26, 1957 2,793,696 Morse May 28, 1957 2,818,118 Dixon Dec. 31, 1957 2,825,408 Watson Mar. 4, 1958 2,874,777 1 Taderna Feb. 24, 1959 FOREIGN PATENTS 200,423 Germany July 17, 1908 

1. A PROCESS FOR INITIATING IN SITU COMBUSTION IN AN UNDERGROUND STRATUM CONTAINING HYDROCARBON MATERIAL COMPRISING PROVIDING A BOREHOLE EXTENDING TO A LOWER LEVEL OF SAID STRATUM AND A TUBING STRING THEREIN EXTENDING TO ADJACENT SAID LEVEL, PACKING THE ANNULUS AROUND THE LOWER END OF SAID TUBING WITH PARTICULATE REFRACTORY MATERILA TO AN UPPER LEVEL OF SAID STRATUM, PASSING A COMBUSTIBLE GASEOUS MIXTURE OF FUEL AND FREE OXYGEN THRU SAID TUBING INTO A LOWER SECTION OF SAID ANNULUS, BURNING SAID MIXTURE AS IT ASCENDS SAID ANNULUS SO AS TO HEAT SAID STRATUM TO COMBUSTION-SUPPORTING TEMPERATURE, VENTING COMBUSTION PRODUCTS THRU SAID BOREHOLE, THEREAFTER INCREASING THE PROPORTION OF FREE OXYGEN IN SAID MIXTURE AS TO BURN A PORTION OF SAID HYDROCARBON MATERIAL AND RETORT A PORTION THEREOF THRU SAID BOREHOLE, SAID REFRACTORY MATERIAL MINIMIZING BY-PASSING OF OXYGEN THRU SAID ANNULUS AND FORCING SAME TO PASS THRU THE COMBUSTION ZONE WITHIN SAID STRATUM AFTER COMBUSTION HAS BEEN INI- 